I. Field of the Invention
This invention relates to methods and apparatus for assembling and forwarding sets of superimposed form sheets, and particularly sets of form sheets which are assembled from form sheets which have been individually and cyclically delivered by an entrance station. The entrance station comprises sensing means for detecting marks provided on the form sheets and for indicating in accordance with the detection of such a mark on a given form sheet that the form sheet belongs to a predetermined set of form sheets. The sets of form sheets are forwarded to downstream processing means at a predetermined cycle frequency. Receiving stations comprising storage devices are provided between the entrance station and the processing means. As used herein, the term "form sheets" describes any paper sheets which are adapted to be assembled in a set thereof and which differ in any feature which can be detected by sensing or scanning.
II. Prior Art and Other Consideraations
Apparatus of the kind described hereinbefore is known from U.S. Pat. No. 4,456,127 (incorporated herein by reference) and comprises two storage devices which are serially arranged in the direction of travel of the sets of form sheets. The individual form sheets are consecutively delivered to the first storage device by an entrance station (which comprises a cutting device). The sets of form sheets are collected in the second storage device and are then forwarded to processing means such as a conveyor or enveloping chain. Because the individual form sheets are temporarily stored in the storage device which directly succeeds the entrance station, the sets of form sheets can be properly assembled even when the forwarded sheets belong to a new set of form sheets (as belateldy indicated by the sensing or scanning means in the entrance station since the operation of the entrance station cannot be interrupted in time before a form sheet belonging to the new set of form sheets leaves the entrance station). In such case the form sheet which belongs to the new set of form sheets can remain in the first storage device until the preceding set of form sheets collected in the second storage device has left that second storage device and has been delivered to the processing means.
If in apparatus of the type described above the cycle frequencies of the entrance station and of the processing means differ greatly, and if the sets of form sheets are composed of different numbers of sheets, and if the cyclic operations of the entrance station and of the processing means are not synchronized, either the operation of the entrance station and/or the processing means must be interrupted. Interruption of operation becomes necessary either because the entrance station is at least temporarily unable to deliver the form sheets at a rate which is sufficient to permit a continuous operation of the processing means, or because the processing means is at least temporarily unable to receive and process the assembled sets of form sheets at a rate which is sufficient to permit a continuous operation of the entrance station.
In view of the foregoing, it is an object of the present invention to provide method and apparatus of the general kind described hereinbefore which facilitates continuous operation of the entrance station and of the processing means even when sets of widely differing numbers of form sheets are being handled.